from enum import Enum


class TokenType(Enum):
    FUNCTION = 'FUNCTION'
    VARIABLE = 'VARIABLE'
    NUMBER = 'NUMBER'
    LEFT_BRACKET = '('
    RIGHT_BRACKET = ')'
    EOF = 'EOF'
    PLUS = '+'
    MINUS = '-'
    MULTIPLY = '*'
    DIVIDE = '/'
    POWER = '^'


def is_token(char):
    return char is not None and char not in ['+', '-', '*', '/', '^', '(', ' ']
